It is well known that use of combustion processes for electrical power generation provides enormous advantages over batteries in terms of energy storage per unit mass and in terms of power generation per unit volume, even when the conversion efficiency in the combustion process from thermal energy to electrical energy is taken into account. For example, hydrocarbon fuels provide an energy storage density between 40 and 50 MJ/kg, whereas even modem lithium ion batteries provide only 0.4 MJ/kg. Thus, even at 5% conversion efficiency from thermal to electrical energy, hydrocarbon fuels provide 5 times higher energy storage density than batteries. Also, the waste products are primarily carbon dioxide and water as compared to toxic metals in the case of batteries. Furthermore, the power generation rate per unit mass or volume of combustion device is orders of magnitude larger than other technologies using chemical reactions, for example, fuel cells. Also, hydrocarbon fuels are relatively inexpensive, readily available, easily stored, and have much longer shelf lives than batteries. Furthermore, combustion-driven devices can use a variety of conventional hydrocarbon fuels without any pre-processing.
Despite these advantages, combustion processes for converting fuel energy to electrical energy have not yet proved practical for powering small scale devices such as cell phones and other portable electronics, which currently rely on batteries. Most approaches to combustion at a small scale use scaled-down versions of macroscopic combustion engines, for example, micro-scale rotary (Wankel) engines, free-piston engines, and micro gas turbine engines. However, when applied at a micro scale, these approaches have numerous difficulties. One of the most fundamental problems limiting combustion at a micro scale is flame quenching due to heat losses when the dimensions of the combustion chamber are too small. For stoichiometric hydrocarbon-air mixtures at atmospheric pressure, the minimum combustion chamber dimension in which flames can exist is about 2 mm when chamber walls are at atmospheric pressure. Furthermore, even if flame quenching does not occur, heat and friction losses become increasingly important at smaller scales since the heat release due to combustion and thus power output scales with engine volume whereas heat and friction losses scale with surface area.
Thus, there remains a need for an efficient microscale combustor that will enable combustion processes to be used for the generation of electrical power for small-scale low-power systems such as micro-electro-mechanical-systems (MEMS) devices, and portable electronic devices such as personal organizers, laptop computers, and wireless phones.